The invention relates to screw pumps and, more particularly, to a screw pump with field refurbishment provisions.
Screw pumps typically comprise at least two screws which extend axially from a suction end to a discharge end, and with helical flights intermeshing with each other during rotation. The screws are typically housed within a screw housing that likewise extends axially from a suction end to a discharge end.
Screw pumps can be classified according to several factors. Two such factors include (1) whether the screw and shaft are separate pieces or are formed as a monolithic unit, and (2) whether the screw is supported from one end only or both ends.
When the screws and shafts are separate pieces, the screws typically slide onto their shafts by means of central bores through the screws, and the conventional prior art method of rotationally fixing each screw to its respective shaft is by use of keys and keyways. When the screw is formed as a monolithic unit with its shaft, the monolithic-unit construction obviates the possibility for keys and keyways needless to say, and the shaft portions may be referred to not as shafts but shaft stubs.
One- and two-piece construction aside, there are two different styles of screw support. Namely, when the screw is supported from one end only, this is referred to as a cantilevered-style screw pumps. While referred to as cantilevered screws, the screw orientation is typically vertical instead of horizontal, with the suction end being high and discharge end low. The shaft (or shaft-stub) for the screw typically projects (depends) from the discharge end, as into a bearing-and-seal carrier, which is where the bearings, seals and drive source are all coupled to the shaft (or shaft stubs). There is no need for any projections beyond the suction end of the screw because there are typically no bearings and no seals at that end of the screw.
The other style of screw support is referred to as simply-supported. Like cantilevered screws, simply-supported screws extend between a suction end and a discharge end. Unlike cantilevered screws, the shafts (or shaft stubs) for simply-supported screws stick out of both ends, because the screw is supported by a bearing at both ends. Simply-supported screws typically also have bearing seals at both ends too.
The shafts for both simply-supported screws as well as for cantilevered screws are typically driven at one end only, and typically this is the portion of the shaft that sticks out the discharge end. Typically, each of the two parallel shafts has a helical gear affixed to it, intermeshing with the helical gear of the other shaft. One shaft is directly driven, and the other shaft is driven off the directly-driven shaft.
Screw pumps of all types have various shortcomings when it comes to service. Screws pumps are most often employed in use environments where they are pumping compressible media, which can be carrying anything from corrosive and/or abrasive materials, to other materials including without limitation materials which leave a coating on the flights of the screws. After extended operation, the screw pumps need to be taken offline and serviced. The screws might need to be withdrawn from the shafts and cleaned or replaced. To do this typically requires extensive disassembly of the screw pump, not only for removal of the screw housing from the bearing-and-seal carrier, but also tearing into the bearing-and-seal carrier too in order to re-time the screws.
Each instance of re-assembly of the screws requires an operation referred to as ‘timing.’ Timing involves adjusting the relative angular orientation of the screws relative to each other for the proper intermeshing and clearance of their respective helical flights during rotation. Again, the shafts typically have helical gears. The helical gears are typically accessed by removing the screw housing from the bearing-and-seal carrier, and then tearing into the bearing-and-seal carrier. At least one helical gear is loosened off its shaft, rotated about its shaft, and then re-tightened in order to properly time the clearance of the flights with each other.
After that, the seals are replaced, the bearing-and-seal carrier is closed back up, the screw housing is re-mounted and so on.
What is needed are improvements in order to simplify the foregoing and overcome shortcomings of the prior art in connection with field refurbishment of screw pumps.